Private Key & Public Key — The Keys to Your ETH

In the world of Ethereum, there are no usernames and passwords. Instead, you control your coins with two cryptographic keys: the private key and the public key. Understanding these means understanding how Ethereum works.

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The Mailbox Analogy

Imagine a glass mailbox: anyone can drop letters in (send ETH to your address) and anyone can see how much is inside (the blockchain is public). But only you have the key to open the mailbox and take letters out (send ETH). That key is your private key.

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Private Key

Your private key is a 256-bit number — a gigantic random number. In hexadecimal notation, it looks like 64 characters (0-9, a-f). Whoever knows your private key has complete control over your Ethereum address and all assets on it.

Private key rules: Never store it digitally. Share it with no one. Never enter it on any website. No legitimate service will ever ask for it.

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Public Key

The public key is derived from the private key through elliptic curve cryptography (secp256k1). It is 128 hex characters long. From the public key, your Ethereum address is derived (the last 20 bytes of the Keccak-256 hash).

Important: from the public key or address, you cannot reverse-compute the private key. The math behind it is a one-way function.

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The Chain: Private Key → Public Key → Address

Private Key (secret) → Public Key (public) → Ethereum Address (public, shortened)

In practice, you rarely see the public key directly. Your wallet shows you the address — and stores the private key securely encrypted. Access to both is controlled through the seed phrase.

→ How to Secure Your Seed Phrase

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Ethereum Specifics: Message Signing

Unlike Bitcoin, you use your private key in Ethereum not only to send ETH, but also to sign messages and transactions for smart contracts. When you use a dApp and MetaMask asks you to "sign," it uses your private key — without revealing it.

Warning: some malicious dApps try to trick you into signing transactions that steal your tokens. Always read what you're signing.

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Last updated: February 2026.